Law of Conservation of Matter, Mass and Energy
The Law of Conservation of Energy states that energy cannot be created or destroyed,
but can change its form.
The total quantity of matter and energy available in the universe is a fixed amount and
never any more or less.The law of conservation of mass or of matter, also known as the
Lomonosov-Lavoisier law, states that the mass of substances in a closed system will remain
constant, no matter what processes are acting inside the system. It is a different way of
stating that though matter may change form, it can be neither created nor destroyed. The
mass of the reactants must always equal the mass of the products.
This law works fine for anything that is not approaching the speed of light; at high speeds,
mass begins transforming to energy (for which reason, we now have the Law of
Conservation of Mass and Energy). However, this means that in most situations the law of
conservation of mass can be assumed valid.
This law was first formulated by Antoine Lavoisier in 1789, but Mikhail Lomonosov in 1748
had also expressed similar ideas earlier. It was the key to making chemistry into a real
science instead of an offshoot of alchemy; prior to this, buoyancy of gases made it
difficult to determine before and after measurements of weight. In nuclear reactions and
in very large astronomical objects, this law becomes questionable. After this, the ideas of
chemical elements, process of fire and oxidation, and many other basic chemical principles
could be understood.
One of the first conservation laws to be discovered was the conservation of mass (or
matter). Suppose that you combine a very accurately weighed amount of iron and sulfur
with each other. The product of that reaction is a compound known as iron(II) sulfide. If
you also weigh very accurately the amount of iron(II) sulfide formed in that reaction, you
will discover a simple relationship: The weight of the beginning materials (iron plus sulfur)
is exactly equal to the weight of the product or products of the reaction (iron(II) sulfide).
This statement is one way to express the law of conservation of mass. A more formal
definition of the law is that mass (or matter) cannot be created or destroyed in a chemical
reaction.
A similar law exists for energy. When you turn on an electric heater, electrical energy is
converted to heat energy. If you measure the amount of electricity supplied to the heater
and the amount of heat produced by the heater, you will find the amounts are equal. In
Law of Conservation of Matter, Mass and Energy
other words, energy is conserved in the heater. It may take various forms, such as
electrical energy, heat, magnetism, or kinetic energy (the energy of an object due to its
motion), but the relationship is always the same: The amount of energy used to initiate a
change is the same as the amount of energy detected at the end of the change. In other
words, energy cannot be created or destroyed in a physical or chemical change. This
statement summarizes the law of conservation of energy.
At one time, scientists thought that the law of conservation of mass and the law of
conservation of energy were two distinct laws. In the early part of the twentieth century,
however, German-born American physicist Albert Einstein (1879–1955) demonstrated that
matter and energy are two forms of the same thing. He showed that matter can change
into energy and that energy can change into matter. Einstein's discovery required a
restatement of the laws of conservation of mass and energy. In some instances, a tiny bit
of matter can be created or destroyed in a change. The quantity is too small to be
measured by ordinary balances, but it still amounts to something. Similarly, a small amount
of energy can be created or destroyed in a change. But, the total amount of matter PLUS
energy before and after a change still remains constant. This statement is now accepted
as the law of conservation of mass and energy.
Examples of the law of conservation of mass and energy are common in everyday life. The
manufacturer of an electric heater can tell consumers how much heat will be produced by a
given model of heater. The amount of heat produced is determined by the amount of
electrical current that goes into the heater. Similarly, the amount of gasoline that can be
formed in the breakdown of petroleum can be calculated by the amount of petroleum used
in the process. And the amount of nuclear energy produced by a nuclear power plant can be
calculated by the amount of uranium-235 used in the plant.
Calculations such as these are never quite as simple as they sound. We think of an electric
lightbulb, for example, as a way of changing electrical energy into light. Yet, more than 90
percent of that electricity is actually converted to heat. (Baby chicks are kept warm by
the heat of lightbulbs.) Still, the conservation law holds true. The total amount of energy
produced in a lightbulb (heat plus light) is equal to the total amount of energy put into the
bulb in the form of electricity.
Law of Conservation of Matter, Mass and Energy